420 APPENDIX 



peculiar relations of the nervous system. These on further 

 inquiry were revealed to me by the minute microscopical 

 investis^ation of these animals. 



This nervous system, in fact, represents the beginning of 

 all nervous systems. It consists, besides nerve- fibres, of 

 nerve-cells, which are scattered over the surface of the animal, 

 and at various points are aggregated so as to form the 

 beginnings of central organs, a number of separate brains. 

 But so slight is the differentiation of the peripheral from the 

 central nervous system, that, under certain necessary conditions, 

 a rudimentary brain of this kind can to some extent develop 

 itself from the scattered nerve -cells in any other position, 

 that is, some other group of nerve-cells can begin to act as a 

 brain. 



Subsequent microscopical researches made by others have 

 confirmed my observations and extended them to other 

 zoophytes. 



Time will not allow me to describe the experiments and 

 researches which I have made on the ribbed Medusse 

 (Ctenophora) — experiments which would of course afford a 

 deeper insight into phenomena of this kind ; I will therefore 

 pass on to another consideration which may throw some light 

 on the question of the definition of the individual in the 

 animal world. 



There are animals which are usually not very appropriately 

 described as colonies. The corals are of this class ; they all 

 arise originally from single beings, each from a simple larva, 

 which begins to divide itself, and ultimately comes to form a 

 colony of numerous individuals, as it is usually expressed. 

 But a coral colony is by no means a co-ordinated whole ; it 

 can be divided up in every direction into these single creatures 

 (polyps), and each will grow into a new colony, a new animal- 

 tree. 



It is much the same with star-fishes and sponges. These 



